Method of forming a glass film on metal



Jan. 30, 1951 s. F. ESSIG 2,539,410

METHOD OF FORMING A GLASS FILM 0N METAL Filed Oct. 6, 1944 2 Sheets-Sheet 1 FIG.3

'AAAAAA/Anmnkg INVENTOR SANFORD F. ESSIG Jan. 30, 1951 s. F. ESSIG 2,539,410

' Y METHOD OF FORMING A GLASS FILM 0N METAL Filed 001;. 6, 1944 I 2 Sheets-Sheet 2 Fl-G.6 2s

34 33 g k W INVENTOR SANFORD F. ESSIG ATTORNEY of the second anode or collector electrode.

Patented Jan. 30,1951

METHOD OF FORMING A GLASS FILM ON METAL Sanford F. Essig, Fort Wayne, Ind., assignor, by mesne assignments,'to Farnsworth Research Corporation, a corporation of Indiana Application October 6, 1944, Serial No. 557,507

3 Claims.

an insulating dielectric material, such as a sheet 1 of mica with a metallic layer which serves as a signal plate. The othersurface of the sheet of mica is provided with a photosensitive cathode consisting of discrete metallic particles. The metallic particles and the signal plate form the two plates of a condenser while the mica serves as the dielectric therebetween.

' In a conventional television picture signal generating tube of the light storage type such a mosaic electrode is bombarded by electrons so that secondary electrons are liberated. A comparatively small portion of the secondary electrons is collected by the second anode or collector electrode of the pickup tube. The larger portion of the secondary electrons, however, is redistributed over the mosaic screen. s In view of the fact that the secondary electrons are not always uniformly distributed over the mosaic they'give rise to an undesired background shading of the television picture reproduced in a receiving tube.

It is, therefore, obvious that it would be desirable to collect substantially all secondary electrons bythe second anode to avoid this.background shading efiect and to increase the sensitivity of the pickup tube. This, however, is not possible with the conventional television pickup tube of the light storage type because the strength of the electric field existing between the mosaic and thesecond anode is too small for that purpose and can not be controlled. The

electric field between the mosaic screen and the second anode is small because the equilibrium potential of the mosaic screen shortly after the electron bombardment is very near the potential Also, the strength of the picture signals generated by the television tube is directly dependent upon the strength of the electric field between the mosaic screen and the second anode until saturation of the secondary electrons takes place.

To overcome this serious drawback of the conventional television picture signal generating tube it has been suggested to use a mosaic screen which has a dielectric layer that is electrically semi-conducting. Such a semi-conductive mosale could be given a biasing voltage to increase 2 the strength of the electric field between the mosaic and the second anode. This field could, for instance, be made of such a strength that all or substantially all of the secondary electrons are attracted and collected by the second anode.

In this manner the electron redistribution problem could be solved and at the same time an increase of the picture signal strength could be obtained.

On the other hand, when the dielectric material which separates the signal plate from the photosensitive cathode is made of a semi-conducting material, part of the charge which is built up and stored on the photosensitive islands of the cathode through the action of the light is dissipated across the dielectric. This, in turn, tends to decrease the strength of the picture signal generated in the television pickup tube. However, theoretical considerationsshow that there is an optimum value for the resistance of the dielectric material separating the signal plate from the photosensitive cathode where the strength of the picture signal is at a maximum. According to these calculations the dielectric layer should have a veryhigh resistance and hence should be made of a semi-conducting material. 7

It is an object of the present invention, therefore, to provide a novel mosaic screen electrode suitable for use in television picture signal generating tubes of thelight storage type.

A further object of this invention is to provide a novel method of forming a semi-conductive film on a metallic support which may be used as a base for a mosaic screen electrode.

In accordance with the present invention there is provided a mosaic screen electrode comprising a thin layer of electrically semi-conducting glass. A metallic foundation is arranged on one surface of the glass layer, and a photosensitive cathode is arranged on the opposite surface of the glass layer. The photosensitive cathode consists of discrete metallic particles.

In accordance with the present invention a base for such a conductive mosaic screen electrode is manufactured by forming a glass film of uniform thickness on a metallic foundation. To this end the metallic foundation is heated to an elevated temperature and molten glass is applied to a surface thereof. The glass is spread over the metallic foundation while the metal and the glass thereon are kept at the elevated temperature. In this manner a glass film of substantially uniform thickness is formed on the metallic foundation.

In accordance with one embodiment of the invention the glass is spread over the metallic foundation by subjecting the foundation with the glass thereon to centrifugal force. In accordance with another embodiment of the invention the molten glass is spread over the surface of the metallic foundation by subjecting the molten glass to the action of a blast of heated gas.

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description, taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the accompanying drawings:

Fig. 1 is a perspective view of a rotating disk used for forming a glass film on a metallic support in accordance with the invention;

.. Fig. 2 is a perspective view of a disk rotating about its center as well as about a point outside of the disk for uniformly distributing molten glass over a metallic support;

Fig. 3 shows a cross-section of a mosaic electrode;

Fig. 4 is a schematic side elevation of a metallic sheet over which a glass layer'is spread out by a hot gas blast;

Fig. 5 is a schematic side elevation of a metallic support over which a glass film is spread, the glass being supplied from a hopper;

Fig. 6 is a schematic side elevation of a metallic support over which a glass film is spread, the molten glass flowing over a rod; and

Fig. '7 is a plan view of a metallic sheet over which a glass film is spread by means of several gas blasts.

Referring now more particularly to Fig. 1 of the drawings, there is shown a disk I which supports a metallic sheet 2 covered by a glass layer 3. Disk i is rotated in any convenient manner in the direction shown by arrow 4. Metallic sheet 2 is first heated up to an elevated temperature, preferably to the temperature of molten glass. Then molten glass is applied to sheet 2 and the sheet with the glass thereon is secured to disk i. When disk I is rotated the centrifugal force will drive off the excess glass from sheet 2. Due to the difference of the centrifugal force acting on the center of sheet 2 and on its rim, the glass tends to be thinner at the center portion than near the edges of sheet 2, as illustrated in Fig. 1. After disk 5 has been brought to rest, sheet 2 is kept at an elevated temperature for a certain time to allow the glass to flow out under the influence of the surface tension of the hot glass and thus spread out in a layer of substantially uniform thickness.

. In order to obtain a more even distribution of the glass by the centrifugal force than is possible with the disk shown in Fig. 1, the metallic sup-- port may be rotated about a point outside of the metallic support. This can, for instance, be accomplished as shown in Fig. 2. Here disk 5 is secured to shaft 8 bearing pulley l. Pulley i is driven by wheel 8 through belt Ill. Wheel 8 is secured to shaft H bearing pulley i2. Pulley i2 is driven by any suitable means not shown here. Rotation of pulley 12 causes rotation of pulley lthrough the intermediary of wheel 8, and hence disk 5 rotates about shaft 6 in the direction indicated by arrow l. Shaft i3 concentric with shaft l I bears pulley l 4 by means of which it may be driven in a suitable manner. Link 15 is secured to shaft I3 and carries at its free end shaft 5 rotatably supported in bearing l6. According- 1y, rotation of pulley Hi causes link 15 to rotate and carry along shaft 6 in the direction indicated by arrows ll.

Metallic sheet 2 secured to disk 5 bears a glass layer s which may be applied thereto as described hereinabove. Rotation of pulleys l2 and M causes metallic sheet 2 and glass layer 3 to rotate about shaft 6 and simultaneously about shaft i3. Hence, the centrifugal forces acting on different points of sheet 2 are practically of equal magnitude and, therefore, glass film 3 will have a substantially uniform thickness. Preferably metallic sheet 2 and glass layer 3 are kept at an elevated temperature approximating the melting temperature of glass until a uniform glass film is formed. In this manner very thin glass films may be obtained having a uniform thickness of the order of magnitude of .001 or less.

In accordance with the invention it is preferred to use an electrically serni-conduoting glass such as what is commercially known as C glass. By making glass film 3 of the required thickness of ap n'oximately .001" a semi-conducting dielectric glass film can be obtained which has a predetermined electric resistance.

A metallic sheet bearing a thin dielectric layer semi conducting glass is admirably suited as a base for conductive mosaic. For obtaining a conductive mosaic, glass layer 3 is provided with a photosensitive cathode consisting of discrete metallic particles shown in Fig. 3. These metallic particles may, for instance, consist of individual silver beads which have been first oxidized and then sensitized with a layer of caesium. Many methods for providing a base with such discrete photosensitive metallic particles are known to those skilled in the art and, therefore, they need not be escribed here. A conductive mosaic, as shown in Fig. 3, may be used in a television pickup tube of the light storage type and will result in an increased picture signal strength. An alternative method of forming a glass film on a metallic foundation has been illustrated in Figs. l to 7. Here the glass is spread over a metallic foundation by means of a blast of hot gas. Referring now to Fig. 4, there is shown a metallic sheet 2 to one surface of which a comparatively thick layer 25 of molten glass has been applied. Preferably metallic sheet 2 is heated to the melting temperature of glass for this purpose. Glass layer 25 is spread out over sheet 2, and the excess glass is driven off by means of a blast of heated gas applied through ipe 26. Preferably a chemically inert gas such as nitrogen is used for removing the excess glass. Sheet 2 is moved under stationary pipe 26 at a uniform rate in the direction indicated by arrow 2?. A film of glass 35 of uniform thickness is formed behind nitrogen blast 26 as clearly shown in Fig. l. Metallic sheet 2 is preferably kept at the melting temperature of glass while the glass is subjected to the action of the hot nitrogen blast. I

Referring now to Fig. 5, there is shown a hopper or container 35 filled with molten glass and from which a stream of molten glass 32 is applied to a predetermined area of metal sheet 2. Metallic sheet 2 is preferably brought to the melting temperature of glass. Sheet 2 is advanced at a uniform speed relatively to pipe 26 and hopper Si in the direction indicated by arrow ill. Pipe 36 applies a hot blast of nitrogen to the area where the molten glass drops down on metal- 110 sheet 2. The hot nitrogen spreads out the glass to form a uniform glass film 30. i

This procedure can be modified as shown in Fig. 6. Here a rod 33 is provided below hopper "3h The molten glass 34 issuing from hopper 3i flows over rod 33 resulting in a more uniform glass stream. The glass is then again spread out by a blast of hot nitrogen supplied by pipe 25. Metallic sheet 2 is advanced at a uniform rate relatively to hopper 3|, nitrogen blast 26 and rod 33, as indicated by arrow 21. During this relative movement, hopper 3|, nitrogen blast 26 and rod 33 are kept at their relative positions so that a glass film 39 of uniform thickness is formed behind nitrogen blast 26.

As shown in Fig. 7 it is also feasible to use a plurality of nitrogen blasts supplied from pipes 35 and 36. The hopper which supplies the molten glass has not been shown in the plan view of Fig. 7. The movement of sheet 2 indicated by arrow 27 takes place in a direction parallel to rod 33. A glass film 39 of uniform thickness is formed behind nitrogen blasts 35 and 36. necessary to move the nitrogen blasts more than once over the metallic surface of sheet 2 in order to cover the entire surface thereof with a glass film of uniform thickness. Preferably sheet 2 is kept at the temperature of molten glass until the formation of the glass film is accomplished.

While therehas been described what are at present considered the preferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. The method of forming a glass film on a It may be metallic member which comprises the steps of heating said metallic member substantially to the temperature of molten glass, applying molten glass to a surface of said metallic member, and mechanically spreading said glass over said metallic member by continuously rotating said member about an aXis through and perpendicular to said member and simultaneously continuously revolving said member about an axis outside said member parallel with said first-mentioned axis while keeping said metal and said glass at the temperature of molten glass to form a glass film of substantially uniform thickness,

2. The method of forming a glass layer on a metallic foundation which comprises the steps of heating said foundation substantially to the temperature of molten glass, applying molten glass to a surface of said metallic foundation, subjecting said foundation and glass simultaneously to two different centrifugal forces applied to and effective laterally upon said molten glass by rotating them in a plane passing through said metallic surface about acenter on said foundation and about a center arranged outside of said foundation and glass while keeping said foundation and glass at said elevated temperature until said glass is distributed over said foundation in a layer of substantially uniform thickness.

3. The method of forming a glass layer on a metallic foundation which comprises the steps of heating said foundation substantially to the temperature of molten glass, applying molten glass to a surface of said metallic foundation, subjecting said foundation and glass to two different centrifugal forces applied to and effective laterally upon said molten glass by rotating them in a plane through said metallic surface about a point arranged outside of said foundation and glass and simultaneously continuously rotating them about a point on said foundation while keeping said fotindation and glass at the temperature of molten glass until said glass is distributed over said foundation in a layer of substantially uniform thickness.

. SANFORD F. ESSIG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 336,157 Putmann et a1 Feb. 16, 1886 862,285 Schmidt Aug. 6, 1907 1,220,552 Provandic Mar. 27, 1917 1,835,113 Iredell Dec. 8, 1931 2,065,570 Essig Dec. 29, 1936 2,092,206 Dudding Sept. 7, 1937 2,146,507 Mayer et a1 Feb. 7, 1939 2,249,007 Kinzie et al July 15, 1941 2,294,760 Morris Sept. 1, 1942 FOREIGN PATENTS Number Country Date 352,911 Great Britain Jan. 9, 1930 

1. THE METHOD OF FORMING A GLASS FILM ON A METALLIC MEMBER WHICH COMPRISES THE STEPS OF HEATING SAID METALLIC MEMBER SUBSTANTIALLY TO THE TEMPERATURE OF MOLTEN GLASS, APPLYING MOLTEN GLASS TO A SURFACE OF SAID METALLIC MEMBER, AND MECHANICALLY SPREADING SAID GLASS OVER SAID METALLIC MEMBER BY CONTINUOUSLY ROTATING SAID MEMBER ABOUT AN AXIS THROUGH AND PERPENDICULAR TO SAID MEMBER AND SIMULTANEOUSLY CONTINUOUSLY REVOLVING SAID MEMBER ABOUT AN AXIS OUTSIDE SAID MEMBER PARALLEL WITH SAID FIRST-MENTIONED AXIS WHILE KEEPING SAID METAL AND SAID GLASS AT THE TEMPERATURE OF MOLTEN GLASS TO FORM A GLASS FILM OF SUBSTANTIALLY UNIFORM THICKNESS. 